1) Preheat the oven to 180C/465F/Gas 4. 2) Grease a 25cm/10in tart tin with butter. 3) Roll out the pastry to line the tart tin, cover with greaseproof paper and fill with baking beans. 4) Put in the oven and bake blind for 10-15 minutes 5) Remove the beans and greaseproof paper and put back in the oven for 4 minutes. 6) Turn the oven up to 200C/400F/Gas 6 7) Meanwhile heat a tablespoon of oil in a frying pan and fry the mushrooms with the thyme until softened. Season well and set aside. 8) Heat a large pan over a medium heat, add the remaining oil and spinach. 9) Cover and allow to wilt, season with the nutmeg. 10) Mix the ricotta and mustard well and season. 11) To complete the tart, spoon the ricotta mixture into the bottom of the pastry case, top with the spinach and then the mushrooms. 12) Pour the whisked eggs over the other ingredients in the tart case. 13) Bake in the oven for 40 minutes until golden brown. 14) Allow to cool slightly before serving.